Head-up display apparatus and image display apparatus thereof

ABSTRACT

A HUD system and light source apparatus can be manufactured with miniaturization at low cost. A head-up display apparatus includes: an image display apparatus generating image light to be projected; an optical system performing predetermined correction to the image light emitted from the image display apparatus; and a concave mirror reflecting the image light corrected by the optical system to project it onto a windshield or combiner. The image display apparatus includes: a solid light source; a collimating optical system converting, into parallel light, the light from the solid light source; a lighting optical system configured by an optical member that polarizes a direction of a light beam generated by the collimating optical system and simultaneously expands a width of the light beam; and a display apparatus, the image display apparatus being configured to be arranged across and opposite the optical system on an optical axis of the concave mirror.

TECHNICAL FIELD

The present invention relates to a technique of a head-up display(hereinafter “HUD”) for: projecting an image(s) onto a windshield of avehicle or onto a combiner as a transparent or translucent, plate-shapeddisplay member provided immediately before the windshield; anddisplaying information to a driver by a virtual image(s). Particularly,the present invention relates to a usable, downsized, highly-efficientimage display apparatus as a light source module generating plane imagelight in the HUD.

BACKGROUND ART

The image display apparatus in a HUD apparatus, which generates theimage light to be projected onto the vehicle's windshield or combinerfor generating the virtual image, is generally incorporated in a narrowspace called a dashboard of the vehicle, and so a new image displayapparatus downsized with high efficiency is desired.

Incidentally, for example, Japanese Patent application Laid-Open No.2015-90442 (Patent Document 1) as a technique related to such a HUDdiscloses a display apparatus that includes a device for displaying animage(s) and a projection optical system for projecting the imagedisplayed on the display device, and that makes screen distortion on theentire viewpoint area of an observer small and realizes miniaturization.Incidentally, the projection optical system of this conventionaltechnique has a first mirror and a second mirror in order of theobserver's optical path from the display device. Then, Patent Document 1discloses that miniaturization of a HUD apparatus is realized by havingsuch a configuration that a relationship among an incident angle of thefirst mirror to a long-axis direction of an image, an incident angle ofthe first mirror to a short-axis direction of the image, an intervalbetween an image display screen of the display device and the firstmirror, and a horizontal width of a virtual image virtually recognizedby the observer complies with a predetermined relationship(s).

RELATED ART DOCUMENTS Patent Documents

Patent Document 1: Japanese Patent Application Laid-open No. 2015-90442

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

Recently, use of a LED (Light Emitting Diode) as a light emitting sourceis effective with improvement of light emitting efficiency of a LED as asolid light source. However, miniaturization and/or modularization of anapparatus have not yet been insufficient in the optical-system formdisclosed in the above-mentioned conventional technique (Patent Document1), which uses a LED collimator for converting the LED and its light tosubstantially parallel light.

Therefore, the present invention has objects of: providing a downsized,highly-efficient image display apparatus preferably usable as a lightsource module that configures a HUD apparatus and generates plane imagelight; and further using the image display apparatus to provide a HUDapparatus suitable for its incorporation into a narrow space called adashboard of a vehicle and for its maintenance.

Means for Solving the Problems

As one aspect for attaining the above purpose, the present inventionprovides a head-up display apparatus projecting image light onto awindshield of a vehicle or a combiner provided just before thewindshield to provide an image to a driver by a virtual image obtainedfrom reflected light of the image light, the head-up display apparatusincluding: an image display apparatus generating the image light to beprojected; an optical system performing predetermined correction to theimage light generated from the image display apparatus; and a concavemirror reflecting the image light corrected by the optical system toproject it onto the windshield or combiner, in which the image displayapparatus includes: a solid light source; a collimating optical systemconverting, into substantially parallel light, light from the solidlight source; a lighting optical system composed of an optical member,the optical member polarizing a direction of a light beam generated bythe collimating optical system and simultaneously expanding a width ofthe light beam; and a display apparatus, and the image display apparatusis arranged across and opposite the optical system on an optical axis ofthe concave mirror.

Effects of the Invention

The present invention makes it possible to realize the image displayapparatus, which is downsized with high efficiency and can bemanufactured at low cost, and to provide, by using the image displayapparatus, the HUD apparatus easily capable of its incorporation intothe narrow space such as a dashboard and its maintenance.

BRIEF DESCRIPTIONS OF THE DRAWINGS

FIGS. 1A-1B are views showing the entire appearance of a head-up display(HUD) apparatus according to a first embodiment of the presentinvention;

FIGS. 2A-2B are views showing an appearance of an image displayapparatus and its internal configuration in the HUD apparatus accordingto the first embodiment;

FIG. 3 is a view showing an appearance of a light source apparatus inthe image display apparatus according to the first embodiment;

FIG. 4 is a view showing an internal configuration of the light sourceapparatus in the image display apparatus according to the firstembodiment;

FIG. 5 is a diagram for explaining details of a collimator in the imagedisplay apparatus according to the first embodiment;

FIGS. 6A-6D are perspective views, cross-sectional views, and enlargedcross-sectional views each showing a detailed shape of a light guide inthe image display apparatus according to the first embodiment;

FIG. 7 is a view showing an operation of an internal optical system inthe image display apparatus according to the first embodiment;

FIGS. 8A-8B are diagrams for explaining details of the light guide inthe image display apparatus according to the first embodiment;

FIG. 9 is a view showing a comparative example for explaining the lightguide in the image display apparatus according to the first embodiment;

FIG. 10 is a view showing a detailed shape of a light guide in an imagedisplay apparatus which is a modification example of the firstembodiment;

FIG. 11 is a view showing a detailed shape of a light guide in an imagedisplay apparatus which is a modification example of the firstembodiment;

FIG. 12 is a diagram for explaining a machining method of a mold usedfor molding a light guide which is a component part of an optical systemin the image display apparatus according to the first embodiment;

FIG. 13 is a view showing a detailed shape of a light guide in an imagedisplay apparatus which is a modification example of the firstembodiment;

FIGS. 14A-14B are characteristic diagrams showing a surface-roughnessspatial frequency distribution of the light guide in the image displayapparatus shown in FIG. 13 ;

FIGS. 15A-15B are views schematically showing light scattering on asurface of the light guide in the image display apparatus shown in FIG.13 ;

FIGS. 16A-16B are plan views showing a shape of a surface of a lightguide in an image display apparatus which is a modification example ofthe first embodiment;

FIG. 17 is a diagram for explaining details of a collimator and acomposite diffusion block in a light source apparatus;

FIGS. 18A-18B are partially enlarged cross-sectional views forexplaining the details of the composite diffusion block in the lightsource apparatus;

FIG. 19 is a view showing a configuration of an image display apparatuswhich is a modification example of the first embodiment;

FIG. 20 is a view showing a configuration of an image display apparatuswhich is a modification example of the first embodiment;

FIG. 21 is a view showing the entire appearance of an image displayapparatus according to another embodiment of the present invention;

FIG. 22 is a view showing an appearance of an internal configuration ofan optical system in an image display apparatus according to anotherembodiment of the present invention;

FIG. 23 is a view showing the entire appearance of an image displayapparatus according to another embodiment of the present invention;

FIG. 24 is a view showing an example of a structure of an optical systemin an image display apparatus according to a second embodiment of thepresent invention;

FIG. 25 is a diagram for explaining the optical system in the imagedisplay apparatus according to the second embodiment;

FIGS. 26A-26B are top views and side views for explaining details of alight guide in the image display apparatus according to the secondembodiment;

FIG. 27 is a diagram showing an example of structures of an LEDcollimator and a polarization conversion prism which are component partsof the optical system of the image display apparatus according to thesecond embodiment;

FIGS. 28A-28B are top views and side views showing details of a lightguide in an image display apparatus which is a modification example ofthe second embodiment;

FIGS. 29A-29B are top views and side views for explaining details of alight guide in an image display apparatus which is a modificationexample of the second embodiment; and

FIGS. 30A-30B are top views and side views for explaining details of alight guide in an image display apparatus which is a modificationexample of the second embodiment.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Hereinafter, embodiments of the present invention will be described indetail with reference to the accompanying drawings. Note that componentshaving the same function are denoted by the same reference charactersthroughout the drawings for describing the embodiments, and therepetitive description thereof will be omitted. Meanwhile, partsdescribed with reference numerals in a certain drawing may be referredto by attaching the same reference numerals although not shown again inthe descriptions of the other drawings.

FIG. 1(a) is a view showing an outline about an example of a motionconcept of a head-up display (HUD) apparatus using an image displayapparatus according to an embodiment of the present invention. A HUDapparatus 1 according to the embodiment of the present invention causesa concave mirror 41 to reflect, via an optical system 43 such as acorrection lens, image light emitted by an image display apparatus 30placed in its housing and to project it onto a windshield 3 of a vehicle2 or a combiner (not shown) provided immediately before the windshield.The image light reflected by the windshield 3 is incident on a viewpointof a driver 5 as shown in FIG. 1(a). This makes it possible for thedriver 5 to view the image light projected onto and reflected from thewindshield 3, and visually recognize an image(s) as a virtual image(s)ahead of the windshield.

Incidentally, particularly, the image display apparatus 30 in such a HUDapparatus 1 generally has an internal configuration as shown also inFIG. 1(b). Here, the image display apparatus 30 indicates a case of aprojector. The image display apparatus 30 includes respective units suchas a light source 301, a lighting optical system 302, and a displayelement 303. More specifically, illumination light generated by thelight source 301 is converged and uniformized (equalized) by thelighting optical system 302, and is irradiated to the display element303. This light includes the display element 303 which is an element forforming a projected image(s) on its display surface and generatingprojected light.

It will be apparent to those skilled in the art that the light emittedfrom the image display apparatus 30 is further projected onto thewindshield 3 of the vehicle 2 via a display distance adjustmentmechanism 400 and a mirror driver 500. Also, adjustment of an angle ofthe concave mirror 41 may makes a display position of the virtual imageviewed by the driver 5 adjustable upward and downward by adjusting aposition of projecting the image onto the windshield 3. Incidentally,content to be displayed as the virtual image is not particularly limitedand, for example, vehicle information, navigation information, an imageof a front scenery photographed with a not-shown camera image(surveillance camera or all-around view), or the like can beappropriately displayed.

FIG. 2(a) is a perspective view showing an external appearance of theHUD apparatus 1, and FIG. 2(b) is a developed perspective view showingeach of its components with them disassembled. As is apparent also fromthese drawings, the image display apparatus 30 configuring the HUDapparatus 1 is generally accommodated inside an exterior case 55 servingas its housing together with the concave mirror 41 and a distortioncorrection lens 43. Then, formed on an upper surface of the exteriorcase 55 is an opening through which image light is projected toward thewindshield. The opening is covered with an anti-glare plate 54 (glaretrap). Additionally, reference numeral 42 in FIG. 2 denotes aconcave-mirror driver composed of an electric motor or the like foradjusting a position of the above concave mirror 41.

Subsequently, the image display apparatus 30 constituting theabove-described HUD apparatus 1 will be detailed below with reference toFIG. 3 . The image display apparatus 30 is configured by accommodatingan LED, a collimator, a composite diffusion block, and a light guide,etc., which are detailed later, inside a light-source apparatus case 11formed of, for example, plastic or the like. A liquid crystal displayelement 50 (corresponding to the display element 303 in FIG. 1 ) isattached to an upper surface of the light-source apparatus case. An LED(Light Emitting Diode) element serving as a semiconductor light sourceand an LED substrate 12 mounting a control circuit of the LED elementare attached to one side surface of the light-source apparatus case.Further, a heatsink 13 for cooling heat generated by the above LEDelement and control circuit is attached to an outside surface of the LEDsubstrate 12.

Incidentally, as is apparent also from the above explanation, thecondition where the HUD apparatus is incorporated into the narrow spacecalled the dashboard of the vehicle will make it apparent for the imagedisplay apparatus 30 in the HUD apparatus 1 to require preferably beingusable by modularization and being miniaturized with high efficiency.

First Embodiment

FIG. 3 is a developed perspective view showing an appearance of an imagedisplay apparatus configuring a HUD apparatus according to a firstembodiment of the present invention. As is apparent also from FIG. 3 ,the image display apparatus (main body) 30 is formed of, for example,plastic or the like, and is configured from a light-source apparatuscase 11 that accommodates therein an LED, a collimator, a compositediffusion block, and a light guide, etc. detailed later. Also, a liquidcrystal display element 50 is attached to an upper surface of thelight-source apparatus case. Further, a LED (Light Emitting Diode)element serving as a solid light source and an LED substrate 12 mountinga control circuit of the LED element are attached to one side surface ofthe light-source apparatus case. Concurrently therewith, a heatsink 13for cooling heat generated by the above LED element and control circuitis attached to an outside surface of the LED substrate 12.

Further, the liquid crystal display element 50 attached to the uppersurface of the light-source apparatus case 11 is configured by a liquidcrystal display panel frame 51, a liquid crystal display panel 52attached to the frame, and a FPC (flexible wiring substrate) 53electrically connected to the panel. That is, although detailed later,the liquid crystal display panel 52 controls image light etc. to bedisplayed thereon by control signals from the LED element serving as asolid light source and from the control circuit (not shown in this case)configuring the HUD apparatus.

FIG. 4 shows a configuration of an optical system that is a portion ofthe internal configuration of the above image display apparatus 30,namely, a configuration of an optical system accommodated in thelight-source apparatus case 11. That is, a plurality (four in thisembodiment) of LEDs 14 a and 14 b (only two are shown in this case)configuring the light source are attached to the LED collimator 15 atpredetermined positions.

<LED Collimator>

Incidentally, each of the LED collimators 15 is formed of, for example,a translucent resin such as acrylic and, as shown also in FIG. 5 , has aconic, convex, outer peripheral surface 151 obtained by rotating asubstantially parabolic disconnection and has at its top portion aconcave portion 153 that forms a convex portion (i.e., a convex lenssurface) 152 at its center portion. Further, the LED collimator 15 hasat a center portion of its planar portion a convex lens surface (or aconcave lens surface recessed inward) 154 projecting to outside. On theother hand, the LEDs 14 a and 14 b are disposed at predeterminedpositions on a surface of the so-called LED substrate 12 which is theircircuit substrate. Incidentally, a paraboloid forming the conical, outerperipheral surface of the LED collimator 15 is set or forms a reflectionsurface within a range of an angle within which light emitted in aperipheral direction from the LED 14 a can be totally reflected insidethe paraboloid. Incidentally, a material for forming the LED collimatoris not limited to acrylic as mentioned above, and any material may beused as long as being a transparent material. A polycarbonate,cycloolefin-based polymer, or silicone-based polymer material, glass,and the like are preferable as a higher heat-resistance material whenpower of the LED is large particularly.

The above LED substrate 12 is arranged on and fixed to the LEDcollimator 15 so that the LEDs 14 a and 14 b on a surface of the LEDcollimator are positioned at central portions of their concave portions153 as shown also in FIG. 5 . The above LED collimator 15 having such aconfiguration: converges, by two convex lens surfaces 152, 154 formingan outer shape of the LED collimator 15, some light beams particularlyradiated upward (in a right direction of FIG. 5 ) from a center portionof the LED collimator among light beams radiated from the LED 14 a,thereby making them parallel; and reflect, by the paraboloid forming theconical, outer peripheral surface of the LED collimator 15, light beamsradiated circumferentially from the other portion of the LED andsimilarly converges them, thereby making them parallel. In other words,the LED collimator 15, whose center portion the convex lens is formed atand whose peripheral portion the paraboloid is formed at, makes itpossible to take out, as a light beam(s) approximating to parallellight, substantially all of light beams generated by the LED 14 a, andto improve use efficiency of the generated light beams.

Incidentally, a rectangular composite diffusion block 16 is provided ona light emission side of the LED collimator 15. That is, the lightemitted from the LED 14 a or 14 b becomes parallel light by an action ofthe LED collimator 15, and is incident on the composite diffusion block16.

Here, returning to FIG. 4 again, a light guide 17 having a substantiallytriangular cross-section is provided via a first diffuser 18 a on anemission surface side of the above composite diffusion block 16, and asecond diffuser 18 b is attached to an upper surface of the light guide.This causes horizontal light of the above LED collimator 15 to bereflected upward in FIG. 4 by an action (workings) of the light guide17, and causes a longitudinal width of a light beam (flux) of thehorizontal light to be expanded by the workings of the light guide 17and guided to an incident surface of the above liquid crystal displayelement 50. Those workings of the light guide 17 make it possible torealize a thin, downsized (compact) image display apparatus.Incidentally, at this time, an intensity of the light is made uniform bythe above first and second diffusers 18 a, 18 b.

<Detailed Structure of Light Guide>

Subsequently, the light guide 17 constituting the above light sourceapparatus will be detailed below with reference to FIG. 6 .Incidentally, FIG. 6(a) is a perspective view showing the entire lightguide 17, FIG. 6(b) is its cross-sectional view, and FIGS. 6(c) and 6(d)are partially enlarged cross-sectional views each showing details of thecross-section.

The light guide 17 is a member formed in a substantially triangularcross-section (see FIG. 6(b)) by a translucent resin such as acrylic. Asis apparent also from FIG. 6(a), the light guide 17 includes: alight-guide light-incident portion (surface) 171 opposing the emissionsurface of the above composite diffusion block 16 via the first diffuser18 a; a light-guide light-reflection portion (surface) 172 forming aslope; and a light-guide light-emission portion (surface) 173 opposingthe liquid crystal display panel 52 of the liquid crystal displayelement 50 via the second diffuser 18 b.

Many reflection surfaces 172 a and connection surfaces 172 b arealternately formed in serrate shapes on the light-guide light-reflectionportion (surface) 172 of the light guide 17 as shown in FIGS. 6(c) and6(d) which are partially enlarged views thereof. Then, the reflectionsurface 172 a (a right-upward line segment in FIG. 6 ) forms an (n:natural number, for example, 1 to 130 in this case) with respect to ahorizontal surface indicated by a dash-single-dot line in FIG. 6 . Asone example, the an is set to 43 degrees or less (but 0 degree or more)in this case.

On the other hand, the connection surface 172 b (a right-downward linesegment in FIG. 6 ) forms βn (n: natural number, for example, 1 to 130in this case) with respect to the horizontal surface. That is, theconnection surface 17 b of the reflection portion is inclined up to anangle which is shadowed with respect to incident light within a range ofa half-value angle of a scattering body described later. Altogetherdetailed later, α1, α2, α3, α4, . . . each form an elevation angle ofthe reflection surface and β1, β2, β3, β4, . . . each form a relativeangle between the reflection surface and the connection surface. As oneexample, the relative angle is set to 90 degrees or more (but 180degrees or less). Incidentally, β1=β2=β3=β4= . . . =β20= . . . β130 inthis case.

FIGS. 7 and 8 each show a schematic view in which sizes of thereflection surface 172 a and the connection surface 172 b are relativelyincreased with respect to the light guide 17 for explanation. A mainlight beam(s) is deflected by δ on the light-guide light-incidentportion (surface) 171 of the light guide 17 in a direction in which anincident angle increases with respect to the reflection surface 172 a(see FIG. 8(b)). That is, the light-guide light-incident portion(surface) 171 is formed in a curved convex shape inclining on a lightsource side. This indicates that parallel light beams from the emissionsurface of the composite diffusion block 16 are diffused through thefirst diffuser 18 a, are incident on the light-guide light-incidentportion (surface) 171, and reach the light-guide light-reflection(surface) 172 while slightly bending (deflecting) upward by light-guidelight-incident portion (surface) 171 as is apparent also from FIG. 8(b)(see a comparative example in FIG. 9 ).

Incidentally, many reflection surfaces 172 a and connection surfaces 172b are alternately formed in serrate shapes on the light-guidelight-reflection portion (surface) 172; and diffusion light beams aretotally reflected on each reflection surface 172 a, verge upward, andare further incident, as parallel and diffusion light beams, on theliquid crystal display panel 52 through the light-guide light-emissionportion (surface) 173 and the second diffuser 18 b. Therefore,reflection-surface elevation angles α1, α2, α3, α4, . . . are set sothat each reflection surface 172 a has an angle equal to or greater thana critical angle with respect to the diffusion light while relativeangles β1, β2, β3, β4, . . . among the reflection surfaces 172 a and theconnection surfaces 172 b are set at the above-mentioned constantangles, more preferably an angle (βn≥90°) of 90° or more although areason(s) for adopting the constant angles is described later.

The above-mentioned configuration is such a configuration that eachreflection surface 172 a always has an angle of a critical angle or morewith respect to the diffusion light. Therefore, even if a reflectionfilm made of metal or the like is not formed on the light-guidelight-reflection portion (surface) 172, total reflection becomespossible and the image display apparatus 30 can be realized at low cost.Meanwhile, as shown in FIG. 9 illustrating a comparative example, when abend (polarization) of the main light beam(s) is absent at thelight-guide light-incident portion of the light guide 17, part of thediffusion light leads to having an angle of a critical angle or lesswith respect to the reflection surface 172 a and sufficient reflectancecannot be secured, so that a light source apparatus with good (bright)characteristics, i.e., an image display apparatus cannot be realized.

Additionally, reflection-surface elevation angles α1, α2, α3, α4 . . .are values which slightly increase as they move from a lower portion ofthe light-guide light-reflection portion (surface) 172 to its upperportion. This is because the light transmitting the liquid crystaldisplay panel 52 of the liquid crystal display element 50 has a certainlevel of divergence angle, particularly for the purpose of preventingoccurrence of a phenomenon in which part of the light transmitting aperipheral portion of the liquid crystal display panel 52 is eclipsed(shaded) by a periphery of a mirror disposed downstream, a so-calledperipheral darkening phenomenon, and because the image display apparatusrealizes such a configuration that light beams near a peripheral portionof the liquid crystal display panel 52 are slightly deflected in acenter-axial direction as shown by light beams L30 in FIG. 7 .

As described above, β1=β2=β3=β4 . . . βn≥90° is set. As shown also inFIG. 12 , this is because when a mold 40 for manufacturing the lightguide 17 by injection molding is machined, the reflection surface 172 aand the connection surface 172 b can be machined simultaneously by endmill having a relative angle β between a bottom surface and a sidesurface. The reflection surface 172 a and the connection surface 172 bcan also be machined with a relatively thick tool(s), so that amachining time can be greatly shortened and machining costs can bedrastically reduced. Further, a boundary edge between the reflectionsurface 172 a and the connection surface 172 b can be machined with highaccuracy, which can improve light-guide characteristics of the lightguide 17.

Also, each of Lr1, Lr2, Lr3, Lr4 . . . of FIG. 7 represents a projectedlength of the reflection surface 172 a to the horizontal surface, andeach of Lc1, Lc2, Lc3, Lc4 . . . represents a projection length of theconnection surface 172 b to the horizontal surface. Lr/Lc, i.e., a ratioof the reflection surface 172 a and the connection surface 172 b areconstitutively variable depending on locations. An intensitydistribution of the main light beams L30 incident on the light guide 17does not necessarily coincide with an intensity distribution to bedesired on an incident surface of the liquid crystal display panel.Therefore, adopted is a configuration in which the intensitydistribution is adjusted by the ratio Lr/Lc of the reflection surface172 a and the connection surface 172 b. Incidentally, as this ratio isincreased, an average intensity of the reflected light at its portioncan be enhanced. Generally, since a center area of the light beams L30incident on the light guide tends to become high in intensity, values ofthe above ratio Lr/Lc are constitutively different depending on placesin order to correct (adjust) the intensity, particularly, the centerarea is set so as to be small in intensity. Since the ratio Lr/Lc variesdepending on locations and the above-mentioned reflection-surfaceelevation angles α1, α2, α3, α4 . . . differ depending on places, anenvelope curve 172 c representing an outer shape of the light-guidelight-reflection portion (surface) 172 shows a curved shape as shown inFIG. 7 .

Further, Lr1+Lc1=Lr2+Lc2=Lr3+Lc3=Lr4+Lc4 . . . =Lr+Lc≤0.6 mm is set inthis case. Adoption of such a configuration makes it possible toequalize repetitive pitches of the reflection surface viewed from thelight-guide light-emission portion (surface) 173 of the light guide 17.Each pitch has a value of 0.6 mm or less, so that when viewed throughthe liquid crystal display panel 52, the individual emission surfacesare viewed as a continuous surface without separation in cooperationwith an action effect of the diffusers 18 a, 18 b. This bringsuniformity of spatial luminance through the liquid crystal display panel52, thereby improving display characteristics. That is, thisconfiguration makes it possible to uniform incident-light intensitydistributions on the liquid crystal display panel 52. On the other hand,if a value of Lr+Lc is less than 0.2 mm, a time of machining the moldbecomes long and concurrently each reflection surface 172 a is difficultto machine with good accuracy. Therefore, the above value is desirably0.2 mm or more.

A shape of the light-guide light-reflection portion (surface) 172 of theabove-described light guide 17 makes it possible to satisfy a totalreflection condition of the main light beams, and to efficiently reflectit without requiring providing a reflection film such as aluminum to thelight-guide light-reflection portion (surface) 172. Therefore, abrighter light source can be realized at low cost without requiringdeposition work etc. of an aluminum thin film that accompanies anincrease in manufacturing costs. Also, each relative angle β is set atsuch an angle that the connection surface 172 b is shadowed with respectto some light beams of the main light beams L30 diffused by thecomposite diffusion block 16 and the diffuser 18 a. This bringssuppression of incidence of unnecessary light beams on the connectionsurface 172 b, thereby making it possible to reduce reflection of theunnecessary light beams and to realize the image display apparatus withgood characteristics.

Further, the above-described light guide 17 makes it possible to freelychange an optical-axis-direction length of the light-guidelight-emission portion (surface) 173 by appropriately setting thereflection-surface elevation angles α1, α2, α3, α4 . . . and the ratioLr/Lc of the reflection surface and the connection surface. Therefore,such an image display apparatus can be realized that a size (screensize) of the light-guide light-emission portion (surface) 173 to thelight-guide light-incident portion (surface) 171 is variable to anappropriately required size (screen size) corresponding to an apparatussuch as the above-mentioned liquid crystal display panel 52. This alsomeans that the light-guide light-emission portion (surface) 173 isformed into a desired shape without depending on arrangement form of theLEDs 14 a, 14 b configuring the light source and thereby a plane lightemitting source having a desired shape can be obtained. Further, thepresent configuration can make thicknesses of the LED collimator 15 andthe composite diffusion block 16 smaller (thinner) with respect to thesize of the liquid crystal display panel 52, and so may be advantageousalso for the miniaturization of the entire apparatus.

Further, as shown also in FIG. 10 , the above-mentioned light guide 17appropriately sets the connection surface 172 b constituting thelight-guide light-reflection portion (surface) 172 (so that light is notreflected to the reflection surface 172 a as part of its center portionin this case). Such setting also makes it possible to extremely changethe ratio Lr/Lc of the reflection surface 172 a and the connectionsurface 172 b on the light-guide light-emission portion (surface) 173 ofthe light guide 17 depending on a location(s). This state is illustratedin an example of FIG. so that the light beams emitted from thelight-guide light-emission portion (surface) 173 of the light guide 17are divided (separated) into right and left sides with respect to theoptical-axis direction. Such a configuration may be suitable for, forexample, a case etc. of separating upward/downward or rightward/leftwardthe illumination light emitted from the HUD apparatus without loss.Further, appropriate adjustment of the ratio Lr/Lc also makes itpossible to partially strengthen or weaken an intensity of the reflectedlight.

Additionally, as shown also in FIG. 11 , if a plurality (two in thiscase) of light source apparatus each including the above-mentioned LEDs14 a, 14 b and light guide 17, etc. are combined so as to oppose eachother in the same surface, the combination makes it possible to realizean image display apparatus including a light-guide light-emissionportion (surface) 173 having further many kinds of surface sizes andlight quantities.

Here, a desirable inclination of the main light beam incident on theliquid crystal display panel is generally close to vertical. However,the main light beam may be inclined by an angle η depending oncharacteristics of the liquid crystal display panel, as shown in FIG. 10. That is, some commercially available liquid crystal panels have goodcharacteristics by tilting an incident angle by about 5° to 10°. In thiscase, however, the above angle η is desirably set to 5° to 10° inaccordance with the characteristics of the panels.

Instead of tilting the panel by the angle η, adjusting the angle of thereflection surface 172 a also makes it possible to tilt the main lightbeam incident on the liquid crystal panel. Further, when the light beamrequires being tilted in a lateral direction of the light guide, therequirement may be realized by: making, rightward/leftward asymmetric,an inclination of a below-detailed triangular texture 161 formed on thelight emission surface of the composite diffusion block 16; or changinga formation direction of a texture composed of the reflection surface172 a and the connection surface 172 b.

Additionally, as shown also in FIG. 13 , if the following functionalscattering surface 175 is added to (formed on) each of the incidentsurface and emission surface of the above-mentioned light guide 17, thediffusers 18 a, 18 b shown also in FIG. 6 may be omitted. Adoption ofthis configuration makes the diffusers 18 a, 18 b unnecessary and makesit possible to realize a reduction in costs of the image displayapparatus.

This functional scattering surface is intended to reduce a unnecessarydivergent component(s) by reducing surface roughness of a component(fine component) having a high spatial frequency. FIG. 14(b) shows asurface-roughness spatial frequency component of a normal scatteringsurface, and FIG. 14(a) shows a surface-roughness spatial frequencycomponent of a scattering surface having more preferable scatteringcharacteristics. As shown in FIG. 14 , a surface-roughness spatialfrequency distribution of the normal scattering surface shows adistribution indicated along a reciprocal (1/f) of the spatialfrequency. In contrast thereto, a spatial frequency distribution of themore preferable surface roughness has low values in a low frequencyregion with a spatial frequency of 10/mm or less and in a high frequencyregion of 100/mm or more. Since the surface-toughness spatial frequencyhas small low frequency components and moderate medium frequencycomponents, a light source with little scattering unevenness can berealized. Also, since the surface-roughness spatial frequency has thesmall high frequency components, a scattering angle of scattered lightdoes not become large and, as shown in FIG. 15(a), a direction of thelight scattered on the functional scattering surface can be limited to adirection usable as a light source, which makes it possible to realizealight source having a bright and uniform luminance distribution.Contrarily, as shown in FIG. 15(b), the normal scattering surfacescatters light in a direction(s) other than a direction usable as alight source, which makes it impossible to realize a bright lightsource.

FIG. 16 is a partially enlarged view showing a specific example of theabove-described texture 161 formed on the incident or emission surfaceof the light guide 17. In this schematic view, FIG. 16(a) shows oneexample in which each boundary between the reflection surface (oremission surface) and the connection surface is arranged and formed in astraight line, and FIG. 16(b) shows another example in which theboundaries are arranged and formed in curved shapes, for example, in astate etc. of being respectively spaced, dispersed, and arranged fromthe LEDs 14 a, 14 b serving as light sources as necessary.

That is, adoption of the above-described functional scattering surfaceleads to an increase of a degree of freedom of control about incidenceand emission of the light at the incident and emission surfaces of thelight guide 17, brings a reduction of luminance unevenness of lightemitted from the light source apparatus, makes it possible to performfine control in accordance with characteristics of an optical-systemapparatus (liquid crystal display element 50 in this case) arranged onits downstream side, and may further be advantageous for a reduction incosts of the apparatus.

<Details of Composite Diffusion Block>

Subsequently, the composite diffusion block 16, which is anothercomponent of the image display apparatus 30, will be described withreference to FIGS. 17 and 18 . Incidentally, FIG. 17 shows a compositediffusion block 16 integrated with the LED collimator 15, and FIGS.18(a) and 18(b) each show a partially enlarged cross-sectional view ofthe composite diffusion block 16.

As is apparent also from FIG. 18(a), many textures 161 each having across-section of a substantially triangular shape are formed on theemission surface of the composite diffusion block 16 formed in aprismatic shape and of a translucent resin such as acrylic. By action ofthe texture 161, the light emitted from the LED collimator 15 isdiffused in a direction that is vertical to the light-guidelight-incident portion (surface) 171 of the above light guide 17 in thedrawing of FIG. 18(a). Then, even if the LED collimators 15 arediscretely arranged due to interaction between the substantiallytriangular texture 161 and the diffusers 18 a, 18 b, the discretearrangement makes it possible to equalize an individual intensitydistribution of the light emitted from the light-guide light-emissionportion (surface) 173 of the light guide 17.

Particularly, the above-mentioned texture 161 makes it possible torestrict the diffusion direction to the lateral direction of the lightguide, and further to control the diffusibility in the lateraldirection. Therefore, the first and second diffusers 18 a, 18 b can beweakened on isotropic diffusibility, which consequently leads toimprovement of light utilization efficiency, and realization of theimage display apparatus with good characteristics. Incidentally, thisembodiment shows, as one example, the substantially triangular texture161 having an angle γ=30 degrees and its forming pitch α=0.5 mm.However, it will be apparent to those skilled in the art that thistexture 161 may utilize the functional scattering surface shown in FIGS.13 to 16 described above. Incidentally, the texture formed on thediffusion block is not limited to a substantially triangular shape, andmay be a concentric circular shape which adapts, for example, a discretearrangement of the LED collimator 15 and the center axis of each LEDcollimator 15.

As shown in FIG. 19 , the composite diffusion block 16 may be alsoreplaced with a so-called wedge-shaped refractive member 16′ having atriangular prism shape instead of the above-mentioned prismatic shape.The refractive member causes the light, which is emitted from the LEDcollimator 15 including the LEDs 14 a, 14 b as light sources, to berefracted in a desired direction (upward in FIG. 19 ), so that the lightcan be made incident also on the flat incident surface of the lightguide 17 by tilting only a desired angle. This brings unnecessity forforming the light-guide light-incident portion (surface) 171 of thelight guide 17 into a curved, convex shape inclined on a light sourceside as shown in FIGS. 5 to 7 , thereby making it possible to ensure thetotal reflection at its reflection surface 172 a. Therefore, a structureof the present embodiment is more easily manufactured.

Additionally, as shown also in FIG. 20 , inclining an arrangement angleof the LED collimator 15 including the LEDs 14 a, 14 b as light sourceswithout providing the above-described composite diffusion block 16 mayalso realize a bright light source (s) by ensuring the total reflectionon the reflection surface 172 a. Incidentally, since the light beam L30emitted from the LED is refracted at the light-guide light-incidentportion (surface) 171 of the light guide 17, an inclination angle δ′ ofthe LED collimator 15 does not necessarily coincide with the inclinationangle δ of the light beam lying inside the light guide 17 (δ′≠δ), and socare should be taken thereof.

As detailed above, the image display apparatus 30 according to the firstembodiment of the present invention makes it possible to further improvethe light utilization efficiency of the light emitted from the LED lightsource and its uniform illumination characteristics and besimultaneously manufactured as a modularized image display apparatus ata small size and at low cost.

Other Embodiments

Meanwhile, FIGS. 21 and 22 show perspective views of the entireappearance and an internal configuration of an image display apparatus300 according to another embodiment of the present invention. In anotherembodiment, the LED collimator 15 that has a plurality of conical,convex shapes and to which the LEDs are attached is attached at aninclined position below the apparatus by utilizing the compositediffusion block 16 b having a substantially trapezoidal cross-section.Incidentally, reference numeral 13 b in FIG. 21 denotes a heatsink forcooling heat generated by the LED element and the control circuit.

FIG. 23 shows a perspective view of the entire appearance of an imagedisplay apparatus 300 according to still another embodiment of thepresent invention. In this embodiment, although not detailed byillustration, such a structure is adopted that the heat generated in theLED substrate 12 propagates through a heat transfer plate 13 d and iscooled by a heatsink 13 c disposed at a lower portion of the apparatus.This configuration makes it possible to realize a light source apparatusshort in the entire length.

Second Embodiment

<Light Source Apparatus Having Polarization Function>

Subsequently, a second embodiment of the present invention will bedetailed below with reference to FIGS. 24 to 30 . Incidentally, thissecond embodiment is different from the first embodiment in an imagedisplay apparatus in which the light from a light source apparatus isemitted as polarization such as S-polarization or P-polarization.However, it is the same as the above to realize a modularized,downsized, highly-efficient image display apparatus usable as a planelight source.

FIGS. 24 to 26 each show a configuration of the image display apparatusaccording to the second embodiment, particularly, a configuration of anoptical system to be its feature. That is, this second embodiment isconfigured so that the number of LEDs 14 a, 14 b constituting the lightsource therein is set at, as one example, two which is one half of thatin the first embodiment, and that a polarization conversion element 21is provided between each LED collimator 15 and the composite diffusionblock 16. Incidentally, the other configurations in the figures are thesame as those in those of the first embodiment, and are denoted by thesame reference numerals, and so their detailed descriptions will beomitted here for avoiding duplication.

Additionally, as is particularly apparent also in FIG. 26(a) out ofthese drawings, the polarization conversion element 21 combines: acolumnar (hereinafter, parallelogrammic pillar), translucent member witha cross-section of a parallelogram extending along a directionperpendicular to the figure; and a columnar (hereinafter, triangularpillar), translucent member with a triangular cross-section, and isformed by arranging a plurality of combinations thereof in an arrayshape and in parallel (in a direction perpendicular to the drawing ofthe figure in this case) to a surface orthogonal to the optical axis ofthe parallel light from the LED collimator 15. Further, a polarizingbeam splitter (hereinafter, abbreviated as “PBS”) film 211 and areflection film 212 are provided alternately at interfaces among thoseadjacent translucent members arranged in the array shape. Additionally,the emission surface to which the light incident on the polarizationconversion element 21 and passing through the PBS film 211 is emitted isequipped with a half wave plate 213.

In this way, the polarization conversion element 21 is configured as asurface (a perpendicular surface extending perpendicularly in thedrawing of the figure) formed by the optical axis of the parallel lightfrom the LED collimator 15 and an extension direction of theparallelogrammic-pillar, translucent member, a so-called symmetricalsurface with respect to the optical-axis surface of the parallel light.Additionally, respective inclinations of the parallelogrammic pillar andthe triangular column of the translucent member, which is a constituentelement thereof, are set to 45 degrees with respect to its optical-axissurface. Then, the polarization conversion element 21 is configured aspolarization conversion elements divided into two sets in aperpendicular direction of the figure with respect to the parallel lightbeams from the two LED collimators 15.

By the polarization converting element 21 configured as described above,as is apparent also from FIG. 26(a), for example, an S-polarization wave(see the symbol (x) in FIG. 26 ) of the incident light, which has beenparallel light by the LED collimator 15 after emission from the LED 14a, is reflected by the PBS film 211, and is further reflected by thereflection film 212 to reach the incident surface of the compositediffusion block 16. On the other hand, after transmitting the PBS film211, a P-polarization wave (see upper and lower arrows in FIG. 26 )becomes an S-polarization wave by the half wave plate 213, and leads toreaching the incident surface of the composite diffusion block 16.

In this way, by the polarization conversion element 21, all of the lightbeams emitted from the LED(s) and converted into parallel light by theLED collimator 15 become S-polarization waves and lead to being incidenton the incident surface of the composite diffusion block 16. Thereafter,the light beams emitted from the emission surface of the compositediffusion block 16 are incident on the above-detailed light guide 17 viathe first diffuser 18 a, are further reflected in an upper direction ofFIG. 26(b) by the action of the light guide 17, and are guided to theincident surface of the liquid crystal display element 50. This flow isthe same as that of the first embodiment. Incidentally, the action ofthe light guide 17 has already been detailed above, and so itsdescription will be omitted here for avoiding duplication.

Incidentally, FIG. 27 is a perspective view showing a state of attachingthe above-mentioned two LED collimators 15 to the polarizationconversion element 21. Further, FIG. 29 is a view showing aconfiguration of an appearance of a composite diffusion block 16 to beattached on an emission surface side of the polarization conversionelement, and FIG. 30 is a side view showing a detailed structure of thecomposite diffusion block 16 and its partially enlarged cross-sectionalview. As is apparent also from these figures, many textures 161 eachhaving a subsequently triangular cross-section are similarly formed onthe emission surface of the composite diffusion block 16 also in thesecond embodiment. However, its details have already been describedabove, and so will be omitted here. Additionally, it will be apparent tothose skilled in the art that, also in this composite diffusion block16, almost the same effect may be achieved by using the functionalscattering surface shown also in FIGS. 13 to 16 as the texture 161 to beformed on its surface.

In this way, the image display apparatus according to the secondembodiment described above converts, into a desired polarization wave(S-polarization wave in this case) by the above-mentioned polarizationconversion element 21, the light incident on the liquid crystal displaypanel 52 constituting the liquid crystal display element 50, therebymaking it possible to attain an effect based on polarizationcharacteristics of the image light to be emitted so as to improve etc.transmittance of the light to the liquid crystal display panel.Therefore, a more downsized, highly-efficient, modularized image displayapparatus can be achieved at low cost by using the less light emittingsource (LED) in number. Incidentally, a case of attaching thepolarization conversion element 21 behind the LED collimator 15 has beendescribed above. However, the present invention is not limited thereto,and it will be apparent to those skilled in the art that almost the sameaction effect are obtained also by providing it in (on the way to) anoptical path reaching the liquid crystal display element.

FIG. 28 shows a configuration of the above-mentioned image displayapparatus in which; the number of LEDs 14 a, 14 b, 14 c constituting thelight source is three; and the polarization conversion element 21 isprovided between each LED collimator 15 and the composite diffusionblock 16, but an orientation control plate 16 c is disposed instead ofthe composite diffusion block 16 constituting the orientation controlplate. Also, this configuration has a feature of using a relativelylarger LED 14 than a shape of the LED collimator 15. In accordancetherewith, a shape of a light incident portion 155 of the LED collimator15 is larger than that of the other embodiments. When explanation ismade with reference to FIG. 28(a), light beams L301, L302 emittedobliquely from the LED 14 a are incident from the light incident portion155 of the LED collimator, are reflected on its side surface 156 likeslightly converged light, and reach the emission surface 157 of the LEDcollimator. Since an outer peripheral portion on the emission surface157 of the LED collimator is particularly formed into a concave surfaceshape, the light beams L301, L302 are refracted and converted intosubstantially parallel light at this concave surface portion and areincident on a light incident portion 21 w of the polarization conversionelement. Adopting this configuration makes it possible to cause thelight from the LED to be efficiently incident on the polarizationconversion element even when a width of the light incident portion 21 wof the polarization conversion element is narrow as shown in FIG. 28(a),so that a highly-efficient light source can be realized.

Subsequently, light beams emitted from the LED 14 a and refracted by thelight incident portion 155 of the LED collimator will be described withreference to FIG. 28(b). Since the light incident portion 155 of the LEDcollimator has a convex shape, the light beam L30 emitted from a centerportion of the LED 14 a is converted into substantially parallel lightat the light incidence portion, passes through the polarizationconversion element 21, and passes through the diffuser 18 a, light guide17, and diffuser 18 b, and is incident on the liquid crystal displaypanel 52. Meanwhile, considering light beams L3001 and L3002 emittedfrom an end portion of the LED 14 a and intersect with each other,particularly, at the center axis, their light beams are incident on thesurface of the light incident portion 155 of the LED collimator at anangle close to perpendicular, and so its refractive angle is small. As aresult, as shown in FIG. 28 , the light beams are emitted in an obliquedirection from the LED collimator 15, and results from being emittedalso from the polarization conversion element in the oblique direction.Therefore, when no member for controlling each direction of the lightbeams exists between the polarization conversion element 21 and thelight guide 17, the above light beams may deviate from the lightincident portion of the light guide 17 like light beams L3001 c andL3002 c indicated by wavy lines, and so cannot be effectively utilized.Contrarily, since the present invention arranges an orientation(alignment) control plate 16 c having a substantially cylindrical convexshape and located between the polarization conversion element 21 and thelight guide 17, the light beams L3001 and L3002 are respectivelyrefracted like the light beams L3001 b and L3002 b and are then incidenton the liquid crystal display panel 52 via the diffuser 18 a, lightguide 17, and diffuser 18 b, so that a highly-efficient light source canbe realized. Particularly, this configuration is suitable for a case ofusing a comparatively larger LED than a width of the light incidentportion of the polarization conversion element. Incidentally, thisconfiguration is not limited to a configuration including thepolarization conversion element 21, and the orientation control plate 16c may be disposed between the LED collimator 15 and the light guide 17.Further, the above configuration omits the diffusers 18 a, 18 b to beprovided on the incident and emission surfaces of the light guide 17,and may also provide (form) the above-mentioned functional scatteringsurfaces (see FIGS. 13 to 16 ) onto their incident and emission surfacesinstead of the omission.

Further, the light guide 17 disposed behind the composite diffusionblock 16 is suitable for a downsized image display apparatus having arelatively small light-source emission surface. Particularly, however,the light guide 17 may be provided directly onto a polarizationconversion element 21′ instead of being disposed behind the compositediffusion block 16 as shown also in FIG. 29 . Incidentally, as isapparent also from FIG. 29 , this configuration is combined by atriangular-column translucent member 211′ and a parallelogrammic-pillartranslucent member 212′ and reflects, at a boundary between them, theS-polarization wave (see the symbol (x) in FIG. 29 ) of the incidentlight that is emitted from the LED 14 a and is to be parallel light.Meanwhile, the configuration forms the PBS film 211 transmitting theP-polarization wave (see upper and lower arrows in FIG. 29 ) and,simultaneously therewith, forms a half wave plate 213 on an uppersurface of the parallelogrammic-pillar translucent member 212′ and areflection film 212 on its side surface.

As is apparent also from FIG. 29 , by the above-mentioned configuration,a polarization component of the incident light, which is emitted fromthe LED 14 a and is to be parallel light by the LED collimator 15, ispolarized to S-polarization by the polarization conversion element 21′replacing the light guide 17, and the incident light leads to beingemitted upward from an upper surface of the element. That is, theabove-described configuration makes it possible to realize remarkablydownsizing of the apparatus and a reduction in the manufacturing costsof the apparatus particularly by removing the light guide 17.

Further, FIG. 30 shows a configuration in which a plurality of sets ofLEDs 14 and LED collimators 15 serving as light sources are arranged notonly horizontally as described above but also vertically. That is, thisembodiment arranges three sets of LEDs 14 and LED collimators 15 apartfrom each other in a lateral direction (see FIG. 30(a)) and,additionally thereto, arranges three sets of LEDs 14 and LED collimators15 adjacent to each other also in a longitudinal direction (see FIG.30(b)). Incidentally, the other configurations in the figure are thesame as those in the second embodiment described above, and so theirdetailed descriptions will be omitted here for avoiding duplication.

Incidentally, such a configuration can arrange many LEDs 14 serving aslight sources in number, and so makes it possible to realize a brighterimage display apparatus. Also, the configuration can further enlarge thelight emission surface, and so is suitable for a case of using an imagedisplay apparatus whose display area has a wide light emission surfaceor using a combination of such an image display apparatus and a liquidcrystal display panel whose display area is wide. Also, for example,such a configuration divides the light emission surface into a pluralityof display areas corresponding to the plural LEDs 14 to independentlycontrol light emitting outputs (lighting) of the LEDs 14, therebyrealizing so-called local diming and further making it possible toincrease contrast of the displayed image and reduce power consumption.Also, such a multi-stage arrangement of the light sources is not limitedonly to the image display apparatus having a polarization function (s)of the second embodiment and, needless to say, almost the same effectcan be obtained also by applying the multi-stage arrangement to theimage display apparatus of the first embodiment.

In addition to the local dimming by controlling the individual LEDsdescribed above, if the above-described control circuit (mounted on aflexible wiring substrate 53 in FIG. 3 , for example) performsindividual control of the LEDs and control of a combination of the LEDsand the liquid crystal display panel 52, performing such control alsomakes it possible to realize a more preferable image display apparatuswith low power consumption and further realize a HUD apparatus using thesame.

Incidentally, a longitudinal arrangement of the LEDs in the local dimingis more preferably an alignment arrangement than a staggeredarrangement. The control of illumination brightness for each place iseasier to perform than that at the alignment arrangement. Also, evenwhen the polarization conversion element is used, the longitudinalarrangement of the LEDs is more preferably the alignment arrangement.When the longitudinal arrangement is changed to the staggeredarrangement, a polarization conversion prism needs to arrange separateelements depending on each longitudinal position while when thelongitudinal arrangement is used, the prism has only to adjust alongitudinal thickness of a single element depending on the arrangementof the LED.

Further, the above description has been made about the liquid crystaldisplay panel having excellent transmittance for the S-polarizationwave. However, it is apparent to those skilled in the art that even whenhaving excellent transmittance for the P polarization wave, thepolarization conversion element having a configuration similar to theabove can obtain the still similar action effect.

Incidentally, as is apparent also from the above detailed description,the modularized, downsized, highly-efficient display apparatus asdescribed above makes it possible to miniaturize a volume of the entireHUD apparatus particularly when being configured so as to oppose on theoptical axis of the concave mirror that reflects the image light toproject it onto the windshield or combiner (however, a correction lensconstituting a correction optical system is interposed therebetween).For this reason, the present embodiment can easily incorporate the HUDapparatus also into a narrow space called a dashboard, and exerts anexcellent effect of further facilitating its incorporation andmaintenance work.

In the above, described have been the image display apparatuses suitablefor use in the HUD apparatuses according to the various embodiments ofthe present invention. However, the present invention is not limitedonly to the above-described embodiments, and includes variousmodifications examples. For examples, the above-mentioned embodimentshave been detailed so as to make the present invention easily understoodand explained, and the present invention is not always limited to theembodiment having all of the described constituent elements. Also, apart of the configuration of one embodiment may be replaced with theconfiguration of another embodiment, and the configuration of oneembodiment may be added to the configuration of another embodiment.Furthermore, another configuration may be added to a part of theconfiguration of each embodiment, and a part of the configuration ofeach embodiment may be eliminated or replaced with anotherconfiguration.

EXPLANATION FOR REFERENCE NUMERALS

-   -   1 . . . HUD apparatus; 2 . . . Vehicle; 3 . . . Windshield; 5 .        . . Driver; 30 . . . Image display apparatus; 41 . . . Concave        mirror; 43 . . . Distortion correction lens; 55 . . . Exterior        case; 54 . . . Antiglare plate; 11 . . . Light-source apparatus        case; 12 . . . LED substrate; 13 . . . Heatsink; 50 . . . Liquid        crystal display element; 51 . . . Liquid crystal display panel        frame; 52 . . . liquid crystal display panel; 53 . . . FPC        (Flexible wiring substrate); 14 a, 14 b . . . LED; 15 . . . LED        collimator; 17 . . . Light guide; 18 a, 18 b . . . Diffuser; 172        a . . . Reflection surface; 172 b . . . Connection surface; 16 .        . . Composite diffusion block; 161 . . . Texture; 21 . . .        Polarization conversion element; 211 . . . PBS film; and 212 . .        . Reflection film.

The invention claimed is:
 1. A head-up display apparatus projectingimage light onto a windshield of a vehicle or a combiner provided beforethe windshield to provide an image to a driver by a virtual imageobtained from reflected light of the image light, the head-up displayapparatus comprising: an image display apparatus generating the imagelight to be projected; and an image projector reflecting the image lightfrom the image display apparatus to project it onto the windshield orthe combiner, wherein the image display apparatus includes a solid lightsource and a display apparatus, and a lighting optical system disposedbetween the solid light source and the display apparatus, the lightingoptical system having a reflection portion that reflects light from thesolid light source in a direction of the display apparatus and a lightemission portion that emits the light reflected by the reflectionportion to the display apparatus, wherein the lighting optical system iscomposed of a plurality of lighting optical systems, wherein thelighting optical systems include: an incident portion, the light beingincident on the incident portion; a reflection portion reflecting theincident light; and an emission portion emitting the light reflected bythe reflection portion, wherein the reflection portion is composed of aplurality of reflection surfaces reflecting the incident light, and aplurality of connection surfaces each connected between the plurality ofreflection surfaces, and wherein the ratio Lr/Lc between lengths Lr andLc is different depending on the location, the length Lr being a lengthof a slope projected in a normal direction with respect to each emissiondirection of the reflection surfaces of the reflection portion, and thelength Lc being a length of a slope projected in a normal direction withrespect to each emission direction of the connection surfaces connectedto the reflection surfaces.
 2. The head-up display apparatus accordingto claim 1, wherein faces of the plurality of lighting optical systemswhich oppose the display apparatus, are arranged so as to become thesame surface.
 3. The head-up display apparatus according to claim 1,wherein the solid light source is configured by one or more lightemitters, and when the solid light source is composed of two solid lightsources, the solid light sources are arranged in the same surface so asto oppose each other.
 4. The head-up display apparatus according toclaim 1, further comprising a collimating optical system converting,into substantially parallel light, light emitted from the solid lightsource, wherein the collimating optical system has a collimator disposedon a light-emission surface side of the solid light source and composedof a translucent member, an outer periphery of the collimator beingformed by a paraboloid, and a lens surface being formed at a centerportion of the collimator.
 5. The head-up display apparatus according toclaim 4, wherein a plurality of solid light sources composed of thesolid light source and a plurality of collimators composed of thecollimator are arranged laterally and arranged longitudinally, and theirarrangement method is an alignment arrangement.
 6. The head-up displayapparatus according to claim 4, further comprising a scattering bodyprovided between the collimating optical system and the lighting opticalsystem, wherein connection surfaces of the light emission portion in thelighting optical system is inclined with respect to the incident lightby such an angle as to be shaded within a range of a half-value angle ofthe scattering body.
 7. The head-up display apparatus according to claim1, wherein the head-up display apparatus has a structure of polarizingthe light between the collimating optical system and the reflectionportion.